When welding two pipe segments together in pipeline construction, it is desirable to minimize or eliminate if possible the amount of oxygen the weld is exposed to. One method of minimizing oxygen in the weld area (i.e., the area proximate the heated welding operation) is to displace the surrounding air (which contains oxygen) in the weld area with a pure or inert gas such as argon. To achieve this displacement, the present invention provides a near-weld purge rig having physical barriers that (together with a portion of the inner surface of the pipe) define a volume or near weld purge channel or purge space into which the inert gas is directed. The rig is then inserted into the pipe segments to be welded such that the purge channel overlaps, coincides with, or is superimposed in the weld area. When the pipe ends are positioned for welding, a gap may exist between them or the ends may be butted so that there is virtually no gap. Now, when the purge channel is filled with inert gas, the weld area is de facto filled with inert gas. Filling the weld area with inert gas means that oxygen is simultaneously being displaced from the weld area. An inert gas supply system is provided which provides a sufficient volume flow rate of inert gas to the purge channel to insure that the purge gas channel pressure is equal to or greater than atmospheric or ambient pressure. Passages between the rig and the pipe or through the gap allow inert gas to exit to the atmosphere so that there is a continuous flow of inert gas from the gas supply system into the channel and then back out either longitudinally down the pipe or out through the pipe gap (i.e., if a gap still exists before welding is complete). An oxygen sensor is positioned in the channel/weld area to track the oxygen concentration in the weld area. When the maximum acceptable oxygen content Omax (e.g., in PPM) is reached, welding can begin.
The present invention also discloses an inert gas delivery system that continues to deliver inert gas at the weld site during welding and proximate the torch. Delivery of the inert gas at the weld site has been determined to have an advantageous cooling effect on pipe weld material when directed at a torch area of the internal surface of the pipe interface. The torch area is a portion of the internal surface of the pipe near the end abutment or gap proximate the portion of the gap or abutment where the torch is welding. Therefore, in addition to displacing oxygen from the weld area, it would be advantageous to provide a near-weld gas delivery rig that directed inert gas at the torch weld area to cool weld pipe material in order to control stability of weld pipe material.